Coupling of δ13C and δ15N to understand soil organic matter sources and C and N cycling under different land-uses and management: a review and data analysis.

This review analyzes the data on co-variations in δ¹³C and δ¹⁵N of soils with land-use types, management, and disturbance obtained from literature to explore potential implications of the dual isotopes in the study of soil organic matter (SOM) sources and C and N processes. Overall, croplands (δ¹³C and δ¹⁵N were − 20.3 ± 4.4‰ and + 7.6 ± 4.4‰, respectively) had greater isotopic values than grasslands (‒26.3 ± 3.0‰ and + 5.4 ± 1.1‰, respectively) and forests (− 26.0 ± 1.1‰ and + 4.3 ± 2.2‰, respectively). For intensively managed lands such as croplands and grasslands, application of organic inputs such as manure and compost of which isotopic signatures differed from the indigenous SOM was the main driver of co-variations in the δ¹³C and δ¹⁵N of SOM. For natural forests, both δ¹³C and δ¹⁵N of SOM co-increased with soil depth, reflecting heavy isotope enrichment during microbial stabilization of SOM and the potential influence of ¹³C-depleted atmospheric CO₂ and ¹⁵N-depleted N deposition on the upper soils. Such vertical co-enrichments of ¹³C and ¹⁵N were disturbed by a land-use conversion to other lands including croplands. Though there were indications that land management practices such as tillage in croplands and grazing in grasslands, land-use changes, and land disturbance including forest fire might also affect both δ¹³C and δ¹⁵N, more data need to be accumulated to find a general trend of the isotopic variations of SOM. Analysis of both δ¹³C and δ¹⁵N may enlarge understanding of changes in SOM sources and soil C and N cycling by land-use types, management, change, and disturbance. [ABSTRACT FROM AUTHOR]